This invention relates to a flexible photovoltaic strip assembly which may be rolled up for storage.
Although photovoltaic power cells have been known in the art since the 1950""s, a drawback to the use of these cells is the fact that they can not be easily stored when not in use.
Japanese Publication No. JP363117472A, publication date May 21, 1998, xe2x80x9cPortable Solar Bell Power Sourcexe2x80x9d, Yanagihara and Z. Ito, describes a power source which can be stored by winding a long, flexible, thin film solar cell onto a winding shaft and placing the wound film in a package.
Further, U.S. Pat. No. 5,605,769, issued Feb. 25, 1997 to D. J. Toms and entitled xe2x80x9cMethod and Apparatus for Supplying Electrical Energy to Battery Powered Equipmentxe2x80x9d discloses an assembly to supply electrical energy to, for example, a rechargeable battery by unfurling, i.e. unwinding, a flexible strip of photovoltaic cells to form a flat surface for exposure of light.
While these devices are useful, there is a drawback in that,
i) if the light converting strip is bent to be coiled, for example, around a rechargeable battery or energy cell, performance degradation in the conversion of light to electricity is likely to occur because of the repeated bending and unbending of the energy cell, particularly when the strip has been coiled and recoiled a number of times, and
ii) coiling the strip around a small diameter such as that of a rechargeable battery or energy cell can produce a permanent set in the strip so that it will not lie flat, in the uncoiled state, for exposure to light.
This invention addresses the need for a photovoltaic strip device which is less likely to suffer performance degradation when coiled and uncoiled, and which is less likely to incur a permanent set when coiled around a small diameter battery or energy cell.
Briefly described, the invention comprises a photovoltaic strip assembly with,
a) a flexible strip substrate of polymeric material,
b) a thin film, voltaic strip bonded to the substrate, and
c) a flexible, substantially transparent, protective covering of polymeric material bonded to the voltaic strip, where the outer surface of the protective covering has a series of transverse, weak joint forming, grooves extending across it.
In this specification rechargeable energy cell includes various rechargeable chemical electron storage media, as well as capacitor and super-capacitor materials and hybrids thereof.
In the preferred embodiment, the depth of the grooves does not exceed 80% of the maximum thickness of the protective covering.
In some embodiments of the present invention, the outer surface of the substrate has a series of transverse, weak joint forming grooves extending across it.
In other embodiments of the present invention the grooves are V-shaped grooves.
The grooves of the protective covering, and the substrate, may form ridges between them in the outer surfaces of the protective covering and the substrate, the ridges of the protective covering and the substrate may be truncated, and the ridges of the substrate may be aligned with grooves of the protective covering, so that the ridges of the substrate will enter the grooves of the protective covering, when the assembly is wound into a coil.
In other embodiments of the present invention, the grooves of the protective covering have curved sides to from dome-shaped ridges between them.
Grooves with curved sides may also be provided in the substrate outer surface to form dome-shaped ridges between them.
In some embodiments of the present invention, when the curved-sided grooves are provided in the protective covering, a series of inwardly curving flutes are also provided in the outer surface of the substrate, extending transversely thereacross, and the flutes are aligned with the domes of the protective covering so that the domes will enter the flutes when the assembly is wound into a coil.
Preferably, the flutes have V-shaped notches between them and the domes and the flutes are shaped to provide substantially continuous curved surfaces when the assembly is wound.
In some embodiments of the present invention the grooves of the protective covering, or the protective covering and the substrate are discontinuous, and the discontinuities of adjacent grooves are displaced across the strip.
In other embodiments of the present invention the grooves of the covering, or the covering and the substrate lie between rows of hump-shaped protuberances.